CVE-2021-23017

Published Jun 1, 2021

Last updated 3 years ago

CVSS high 7.7
Openresty
Port (443)

Overview

Description
A security issue in nginx resolver was identified, which might allow an attacker who is able to forge UDP packets from the DNS server to cause 1-byte memory overwrite, resulting in worker process crash or potential other impact.
Source
f5sirt@f5.com
NVD status
Modified

Risk scores

CVSS 3.1

Type
Primary
Base score
7.7
Impact score
5.5
Exploitability score
2.2
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
Severity
HIGH

CVSS 2.0

Type
Primary
Base score
6.8
Impact score
6.4
Exploitability score
8.6
Vector string
AV:N/AC:M/Au:N/C:P/I:P/A:P

Weaknesses

f5sirt@f5.com
CWE-193
nvd@nist.gov
CWE-193

Social media

Hype score
Not currently trending

  1. Malicious (99%) https://t.co/7ShGmdeM5d Product Nginx CVE-2021-23017 CVE-2021-3618 CVE-2022-3638 CVE-2023-44487 https://t.co/yJfVvQJJqQ https://t.co/hT3w7fzIsY

    @KulinskiArkadi

    4 Jul 2025

    63 Impressions

    1 Retweet

    0 Likes

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  2. CVE-2023-44487 CVE-2021-23017 CVE-2021-3618 141.95.17.178 port 22 | 80 | 9100 #Anonymous

    @saw11b

    12 Apr 2025

    43 Impressions

    0 Retweets

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  3. {"cpes":openbsd:openssh:8.4p1","cpe:/o:debian:debian_linux","cpe:/a:f5:nginx:1.18.0"],"hostnames":["https://t.co/KQeBMZwqHr",],"ip":"23.95.39.61","ports":[21,22,80,443,5222,5269],"tags":["eol-product"],"vulns":["CVE-2023-44487","CVE-2021-23017","CVE-2021-3618"]}

    @portknock

    10 Mar 2025

    6 Impressions

    0 Retweets

    0 Likes

    0 Bookmarks

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  4. {"hostnames":["https://t.co/lsjL6hNT8q","https://t.co/Lurbv4tXGG"],"ip":"104.131.14.208","ports":[22,25,80,443,3000,3001],"tags":["cloud","self-signed","starttls","eol-product"],"vulns":["CVE-2021-23017","CVE-2021-3618","CVE-2023-44487"]}

    @ClumsyLulzReal

    17 Nov 2024

    4 Impressions

    0 Retweets

    0 Likes

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Configurations

Related CVEs

  1. Issue summary: ChaCha20-Poly1305 and AES-OCB decryption with an empty ciphertext can report success without verifying the supplied authentication tag when the operation is finalized by calling the EVP_Cipher() function. Impact summary: Applications calling EVP_Cipher() on an empty ciphertext and expecting the call to check the AEAD tag may accept forged messages. CWE: CWE-354 (Improper Validation of Integrity Check Value) Description: The EVP_Cipher() API call for AEAD ciphers behaves like a one shot encryption and decryption call. It also verifies the AEAD tag after the decryption operation. However for AES-OCB and ChaCha20-Poly1305 ciphers it skipped the AEAD tag verification when an empty ciphertext was passed to the function. The callers of this function might believe that a successful return indicates a valid AEAD tag for these ciphers, even when that has not truly been validated in this case. FIPS impact: no The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this CVE as the affected algorithms are not FIPS approved and thus not implemented in the FIPS module.•CVE-2026-75803
  2. Issue summary: Receiving a DTLS record for a future epoch while a handshake is in progress causes OpenSSL to buffer far more memory than the record itself requires. Impact summary: A peer can use a small amount of network traffic to make an OpenSSL DTLS endpoint retain a disproportionately large amount of memory, which may lead to a Denial of Service. CWE: CWE-405: Asymmetric Resource Consumption (Amplification) Description: While a DTLS handshake is in progress, a peer may legitimately have already moved on to the next epoch (for example, having sent its ChangeCipherSpec and Finished messages) before the local endpoint has processed the same transition, typically because of reordering on the underlying UDP transport. OpenSSL buffers such early records so that they can be processed once the local endpoint catches up. Buffering a record currently retains the entire read buffer it arrived in, which is sized to hold the largest possible DTLS record (around 16 kilobytes), rather than just the bytes that make up the record itself. Up to 100 such records may be buffered per connection. As a result, a peer that sends a stream of small forged records claiming to belong to the next epoch can cause an OpenSSL DTLS endpoint to retain around 1.7 megabytes of memory, despite sending only a small fraction of that amount of data over the network. An attacker therefore gains a memory amplification factor of around 1200, and can multiply the effect across as many associations as it is able to open, making this a remote memory exhaustion Denial of Service risk for DTLS servers. Since the memory retained per connection remains bounded, and any limit an application already places on the number of concurrent associations also bounds the total exposure, this issue has been assessed as Low severity. FIPS impact: no No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary. OpenSSL 4.0, 3.6, 3.5, 3.4, 3.0, 1.1.1 and 1.0.2 are vulnerable to this issue. OpenSSL 4.0 users should upgrade to OpenSSL 4.0.2. OpenSSL 3.6 users should upgrade to OpenSSL 3.6.4. OpenSSL 3.5 users should upgrade to OpenSSL 3.5.8. OpenSSL 3.4 users should upgrade to OpenSSL 3.4.7. OpenSSL 3.0 users should upgrade to OpenSSL 3.0.22. Premium support customers only: OpenSSL 1.1.1 users should upgrade to OpenSSL 1.1.1zi OpenSSL 1.0.2 users should upgrade to OpenSSL 1.0.2zr This issue was reported on 18 May 2026 by Amazon Web Services. The fix has been developed by Matt Caswell. -- cut (non-publishing metadata for internal use) -- Reported by: Amazon Web Services Fixed by: Matt Caswell•CVE-2026-54874
  3. Missing validation of the outer content_type byte on TLS 1.3 encrypted records in s2n-tls allows an active man-in-the-middle to silently discard individual application data records without either endpoint detecting the modification. RFC 8446 Section 5.2 requires that the outer content_type of all encrypted TLS 1.3 records must be application_data (0x17). The s2n-tls AEAD implementation hardcodes this value in the additional authenticated data rather than using the actual wire byte, so the outer content_type is not covered by the authentication tag. This enables selective suppression of application data. In HTTP pipelining scenarios, dropping a TLS record containing an HTTP request can cause request/response desynchronization, where subsequent responses are delivered to the wrong requests. In write-heavy workloads, a dropped record containing a write request can result in undetectable data loss when the client interprets a subsequent success response as confirmation of the dropped write. All TLS 1.3 connections are affected. Both TLS clients and servers are affected. TLS 1.2 and QUIC connections are not affected. We recommend you upgrade s2n-tls to version v1.7.6•CVE-2026-16317
  4. The QUIC transport parameters extension handler in s2n-tls incorrectly uses s2n_alloc instead of s2n_realloc to store the peer's transport parameters. When a TLS 1.3 connection goes through a HelloRetryRequest, the handler is called twice on the same connection. On the second call, s2n_alloc zeroes the existing pointer before allocating new memory, causing the first allocation to be leaked. This can occur during normal QUIC traffic when a client offers a key share group the server does not prefer. An unauthenticated user can amplify the issue by deliberately forcing HelloRetryRequests, causing up to approximately 64 KB of unreachable memory per handshake. Over time, this can lead to increased memory consumption on long-running server processes. The unreachable memory is only reclaimed when the process is restarted. Only server-side QUIC-enabled deployments are affected. Non-QUIC TLS connections are not affected. We recommend you upgrade s2n-tls to version v1.7.6•CVE-2026-16318
  5. NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_slice_module module. When the slice directive and unnamed regex captures are configured or when a background cache update happens, unauthenticated attackers can send requests that may cause uninitialized memory access in the NGINX worker process, leading to limited disclosure of memory or a restart. Impact: This vulnerability may allow remote, unauthenticated attackers to have limited control to disclose memory contents or restart the NGINX worker process. There is no control plane exposure; this is a data plane issue only. Note: The ngx_http_slice_module module is not enabled by default; it's enabled with the --with-http_slice_module configuration parameter. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.•CVE-2026-60005

References

Sources include official advisories and independent security research.